Apparatus and method for obtaining subject information, display method, and program

ABSTRACT

A subject-information acquisition apparatus includes a light source; a holding member configured to hold a subject so as to surround the subject; at least one transducer configured to receive an acoustic wave generated by irradiating the subject with light from the light source; and a signal processing unit configured to obtain distribution information using a received signal output from the transducer. The holding member includes a marker that absorbs the light and generates an acoustic wave.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an apparatus and a method for obtainingsubject information, a display method, and a program for the same. Inparticular, the present invention relates to a technique using acousticwaves generated by light irradiation.

Description of the Related Art

There is a photoacoustic imaging (PAI) technique for imaging tissue in asubject using a photoacoustic effect that, when the subject isirradiated with pulsed light generated from a light source, acousticwaves are generated in the subject due to absorption of the pulsedlight.

International Publication No. WO/2010/030817 discloses an apparatus witha configuration in which a plurality of transducers that receiveacoustic waves generated in a subject are disposed on a hemisphericalsupporting member. In examination, the subject is held by a thincup-shaped holding member. Between the holding member and thetransducers, an acoustic medium, such as water, through which acousticwaves can propagate is provided. Light is radiated from below asupporting member onto the subject through the holding member and theacoustic medium. Acoustic waves generated in the subject reach thetransducers through the holding member and the acoustic medium.

Apparatuses including a holding member that holds a subject so as tosurround the subject, as disclosed in International Publication No.WO/2010/030817, have an advantage in the viewpoint of usability that aload exerted on a person to be examined (hereinafter also referred to asan examinee) is low. On the other hand, an image presented to anexaminer needs further improvement.

SUMMARY OF THE INVENTION

A subject-information acquisition apparatus according to a first aspectof the present invention includes a light source; a holding memberconfigured to hold a subject so as to surround the subject; at least onetransducer configured to receive an acoustic wave generated byirradiating the subject with light from the light source; and a signalprocessing unit configured to obtain distribution information using areceived signal output from the transducer. The holding member includesa marker that absorbs the light and generates an acoustic wave.

A method for displaying an image on a display unit according to a secondaspect of the present invention includes the steps of generatingdistribution information using a received signal caused by acousticwaves generated from a subject irradiated with light and a receivedsignal caused by acoustic waves generated from a marker irradiated withlight, the marker being provided on a holding member that holds thesubject; and displaying the distribution information.

A method for obtaining subject information according to a third aspectof the present invention includes the steps of setting a sound velocityin an acoustic medium between a holding member that holds a subject anda transducer using a received signal caused by an acoustic wavegenerated from a marker irradiated with light, the marker being providedon the holding member; and generating the distribution information usinga received signal caused by an acoustic wave generated from the subjectirradiated with light and information on the sound velocity.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the configuration of asubject-information acquisition apparatus of a first embodiment.

FIG. 2A is a schematic side view of a holding member.

FIG. 2B is a schematic top view of the holding member.

FIG. 3A is a schematic side view of another holding member.

FIG. 3B is a schematic top view of the holding member.

FIG. 4 is a schematic diagram of a subject-information acquisitionapparatus of Example 2.

FIG. 5A is a schematic diagram illustrating first distributioninformation.

FIG. 5B is a schematic diagram illustrating second distributioninformation.

FIG. 6A schematically shows tomograms of second distribution informationin which no guide is displayed.

FIG. 6B schematically shows tomograms of second distribution informationin which a guide is superimposed.

FIG. 7A is a schematic side view of another holding member.

FIG. 7B is a schematic top view of the holding member.

FIG. 8 is a schematic diagram of a subject-information acquisitionapparatus of a second embodiment.

FIG. 9A is a schematic side view of another holding member.

FIG. 9B is a schematic top view of the holding member.

FIG. 10A is a schematic diagram of a two-dimensional image obtained whena sound velocity is properly set.

FIG. 10B is a schematic diagram of a two-dimensional image obtained whena sound velocity different from an actual sound velocity is set.

FIG. 11 is a flowchart for explaining the processes of Example 8.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described with reference tothe drawings. Like components are denoted by the same reference signs,and descriptions thereof are omitted.

A subject-information acquisition apparatus according to an embodimentof the present invention obtains characteristic information indicatingcharacteristic values corresponding to an individual plurality ofpositions in a subject using signals obtained by receiving acousticwaves. The acquired characteristic information reflects the absorptivityof light energy. Specific examples of the characteristic informationinclude characteristic information that reflects the initial soundpressure of the generated acoustic waves, a light energy absorptiondensity derived from the initial sound pressure, absorption coefficient,and the concentrations of constituents of the tissue. Examples of theconcentrations of constituents include oxygen saturation, totalhemoglobin concentration, and oxyhemoglobin or deoxyhemoglobinconcentration. Two- or three-dimensional distribution information may begenerated from characteristic information on a plurality of positions.The distribution information may be generated in the form of image data.

The subject-information acquisition apparatuses according to thefollowing embodiments are mainly used for diagnoses of malignant tumorsor blood diseases of humans and animals and observation of the progressof chemical treatment. Thus, supposed subjects include part of livingorganisms, specifically, objects to be examined, such as the breasts ofhumans and animals.

First Embodiment

The configuration and process of a subject-information acquisitionapparatus of a first embodiment will be described.

Overall Apparatus Configuration

FIG. 1 is a schematic diagram illustrating the configuration of thesubject-information acquisition apparatus of the first embodiment. Thesubject-information acquisition apparatus of this embodiment includes atleast a light source 121, a plurality of transducers 115 that receiveacoustic waves, a holding member 109 that holds a subject 103, and asignal processing unit 133 that obtains characteristic information onthe interior of the subject 103 using received signals from thetransducers 115.

Light from the light source 121 is transmitted through a lighttransmitting portion 123 and exits from a light emitting portion 125.The exiting light irradiates the subject 103 through acoustic matchingliquid (acoustic medium) 119 and the holding member 109. Acoustic wavesgenerated at a plurality of positions in the subject 103 by theirradiation of light reach the plurality of transducers 115 through theholding member 109 and the acoustic matching liquid 119.

The plurality of transducers 115 individually receive acoustic waves andoutput time-series received signals. The received signals are input to asignal collecting unit 131. The signal processing unit 133 generatesdistribution information including characteristic information on theinterior of the subject 103 using signals output from the signalcollecting unit 131.

Light Source 121

The light source 121 may be a pulsed light source capable of generatingpulsed light of the order of nanoseconds to microseconds. Specifically,a pulse width of the order of 1 to 100 nanoseconds is set to efficientlygenerate acoustic waves. A preferable wavelength is from 600 nm to 1,100nm. Specific examples of the light source 121 may be pulse lasers, suchas an Nd:YAG laser and an alexandrite laser. Other examples are a Ti:salaser and an OPO laser that uses Nd:YAG laser beam as exciting light. Inaddition, a semiconductor laser may be used. The light from the lightsource 121 is transmitted to the light emitting portion 125 through thelight transmitting portion 123. The light transmitting portion 123 maybe an optical system, such as a lens, a mirror, or an optical fiber. Thelight emitting portion 125 may be an optical system, such as a diffuseror a lens. The light emitting portion 125 is integrated with asupporting member 113.

Supporting Member 113

The supporting member 113 is a member that fixedly supports theplurality of transducers 115. As shown in FIG. 1, the supporting member113 has a bowl-shaped portion having a spherical surface. Receivingportions of the plurality of transducers 115 are disposed at the innerwall of the bowl-shaped portion. The supporting member 113 has a frameportion 117 larger than the diameter of the bowl-shaped portion at thesubject side with respect to the bowl-shaped portion. For examination,the bowl-shaped portion and the frame portion 117 are filled with theacoustic matching liquid 119 serving as an acoustic medium. The acousticmatching liquid 119 is composed of a material having an acousticimpedance close to that of human bodies to cause little attenuation ofacoustic waves. For example, the acoustic matching liquid 119 preferablyhas an impedance of 1.3 MRayls or higher and 2 MRayls or lower. Specificexamples include water and oil.

The supporting member 113 is disposed on a stage 127. A moving mechanism129 can move the supporting member 113 in an X-Y plane (in a horizontaldirection) relative to the subject 103. The moving mechanism 129includes a motor, such as a stepping motor. The path of the movement ofthe supporting member 113 may be a two-dimensional spiral path or alinear path. The moving mechanism 129 may move the supporting member 113in the Z-direction or rotate the supporting member 113 about apredetermined axis. As described above, the supporting member 113includes the light emitting portion 125, so that light is radiated frombelow the subject 103.

Transducers 115

The transducers 115 may any other transducers that receive acousticwaves and convert them to electrical signals, such as piezoelectricdevices using a piezoelectric phenomenon of lead zirconate titanate(PZT), transducers using interference of light, and capacitivetransducers, such as capacitive micromachined ultrasonic transducers(CMUTs).

The plurality of transducers 115 are disposed, with the receivingsurfaces along the spherical surface of the bowl-shaped portion. Thepattern of disposition may be a pattern in which the plurality oftransducers 115 are disposed in a three-dimensional spiral, as disclosedin International Publication No. WO/2010/030817. The disposition alongthe spherical surface allows a configuration in which directions of highreceiving sensitivity of the transducers 115 point to specific areas.

Typically, the normal directions of the receiving surfaces (frontsurfaces) of the transducers 115 have the highest receiving sensitivity.Thus, disposing the transducers 115 along the spherical surface allowsdirections in which the receiving sensitivity of the transducers 115 ishigher than a predetermined level to point to the vicinity of the centerof curvature (a specific area) of the hemispherical bowl-shaped portion.In particular, the plurality of transducers 115 may be disposed so thatdirections of the highest sensitivity intersect in the vicinity of thecurvature of the bowl-shaped portion.

In this embodiment, the resolution of an area to which directions inwhich the receiving sensitivity of the transducers 115 is higher than apredetermined level point can be enhanced. In this specification, suchan area capable of high sensitivity reception is referred to as ahigh-sensitivity area, and the high-sensitivity area results in highresolution. The high-resolution area may have the highest resolution tohalf the highest resolution. Specifically, a diameter r in Eq. (1) isthe diameter of the high-resolution area.

where R is an allowable resolution, R_(H) is the highest resolution, r₀is the diameter of a sphere on which the transducers 115 are disposed,and Φ_(d) is the diameter of each transducer 115.

In this embodiment, the disposition of the plurality of transducers 115is given for illustration, and any other dispositions that allow adesired high-sensitivity area are possible. The disposition allowing thehigh-sensitivity area is a disposition that allows acoustic waves to bereceived with higher sensitivity than a disposition in which directionsof the highest sensitivity of the transducers 115 are parallel to eachother. The high-sensitivity area determined depending on the dispositionof the plurality of transducers 115 is formed at an area in which thesubject 103 is supposed to be placed for examination.

Specifically, the plurality of transducers 115 may be disposed so thatthe directions of the highest receiving sensitivity of at least two ofthe transducers 115 point to a specific area. In other words, thetransducers 115 may be disposed so that the direction of the highestreceiving sensitivity differs between part of the plurality oftransducers 115 and another transducer 115 and that the directions ofthe highest receiving sensitivity point to a specific area. Thedirections of the highest receiving sensitivity of at least part of theplurality of transducers 115 may intersect one another.

Since the directions of the highest receiving sensitivity point to aspecific area, acoustic waves generated from the specific area can bereceived with higher sensitivity than that when the directions of thehighest receiving sensitivity of the transducers 115 are parallel. Thiscan enhance the resolution of an image in the specific area as comparedwith that when the directions of the highest receiving sensitivity ofthe transducers 115 are parallel.

In other words, such a disposition allows the directional axes (axesalong the directions of the highest receiving sensitivity) of at leastpart of the plurality of transducers 115 to be converged.

In other words, such a disposition is such that the receiving surfacesof the transducers 115 face the interior of the supporting member 113.That is to say, in the case where the transducers 115 are disposed on asupporting member having a curved surface, such as a spherical surface,the receiving surfaces of the transducers 115 are disposed along asurface adjacent to the center of curvature. In the case where thetransducers 115 are disposed on a supporting member having a surfaceformed of a plurality of flat surfaces (angles that the flat surfacesform are obtuse angles), the receiving surfaces are disposed along theinner surface (a recess-side surface).

In this specification, “spherical surface” includes spherical surfacesother than the surface of a true sphere. In other words, “sphericalsurface” includes a spherical surface having an opening, such as ahemispherical surface. “Spherical surface” further includes a surfacehaving surface irregularities to the extent that it is regarded as aspherical surface and the surface of an ellipsoid (a three-dimensionalfigure of an ellipse, whose surface is a quadratic surface) that can beregarded as a spherical surface.

Holding Member 109

The holding member 109 is disposed in an opening of a bed 105 on whichan examinee 101 is laid face-down (prone position). A breast, which isthe subject 103, is inserted through the opening and is held by theholding member 109. The holding member 109 holds the subject 103 so asto surround it. “Surround the subject” does not necessarily refer tosurrounding all the directions of the subject 103. The holding member109 may be a cup-shaped member, which allows the subject 103 to besupported from below in the direction of gravity.

The holding member 109 may be formed of a material having an acousticimpedance close to that of a human body. For example, the holding member109 may have an acoustic impedance of 1.3 MRayls or higher and 2 MRaylsor lower. The use of a material having such characteristics can reducethe reflection of acoustic waves at the interface between the subject103 and the holding member 109. To reduce noise due to multiplereflection of acoustic waves, the holding member 109 may be thin. Forexample, the holding member 109 preferably has a thickness of 100 μm orless. Since light irradiates the subject 103 through the holding member109, the holding member 109 may be formed of a material having hightransmittance of light in a wavelength band used (preferably, 90% orhigher). Specific examples of the material of the holding member 109include polymethylpentene and polyethylene terephthalate.

The holding member 109 of this embodiment includes a marker 111 which isa light absorber that absorbs light to generate acoustic waves. Themarker 111 has a higher light absorption coefficient than that of thecup-shaped portion of the holding member 109. In this embodiment, theuse of received signals caused by the acoustic waves generated from themarker 111 can enhance the visibility of images (images displayed on adisplay unit 506) presented to the examiner or operator who is a user.An example of the marker 111 is a light absorber colored in black orgray. However, an excessive intensity of acoustic waves generated fromthe marker 111 can cause noise in obtaining characteristic informationon the subject 103. Thus, the intensity of acoustic waves generated fromthe marker 111 may be equal to or one place less than the intensity ofacoustic waves generated from the subject 103. The marker 111 preferablyhas an absorption coefficient of 0.05/mm or more and 1.0/mm or lessconsidering that the absorption coefficient of hemoglobin, which is atypical substance that absorbs light in the subject 103, is between0.3/mm and 0.9/mm.

The shape of the marker 111 may be selected depending on the use; forexample, a dotted pattern, a line pattern, a matrix pattern, a radiatingpattern, and a circular pattern.

Signal Collecting Unit 131

A signal collecting unit 131 is a circuit that collects time-seriesreceived signals output from the individual transducers 115 channel bychannel. The signal collecting unit 131 may be a circuit generallyreferred to as a data acquisition system (DAS). Specifically, the signalcollecting unit 131 includes an amplifier that amplifies receivedsignals, an A-D converter that converts received analog signals todigital signals, and a memory that stores the received signals.

The signal processing unit 133 obtains distribution informationincluding characteristic information on the interior of the subject 113using received signals output from the signal collecting unit 131.Specifically, the signal processing unit 133 includes a reconstructingportion 433 that reconstructs images using the channel-by-channelreceived signals. Examples of a method for reconstructing images includeknown reconstructing methods, such as universal back projection (UBP)and filtered back projection (FBP) disclosed in U.S. Pat. No. 5,713,356.The image reconstruction allows the distribution of channel-by-channeltime-series received signals on two- or three-dimensional coordinateaxes (distribution corresponding to the space in the subject 103) to begenerated. Examples of the reconstructing portion 433 include a CPU, agraphics processing unit (GPU), a field programmable gate array (FPGA)chip.

The signal processing unit 133 may include a signal storing portion 401that stores received signals output from the signal collecting unit 131.Typical examples of the signal storing portion 401 are storage mediums,such as a ROM, a RAM, and a hard disk. The signal storing portion 401may be either a single storage medium or a plurality of storage media.

Image Processing Unit 134

An image processing unit 134 generates image data to be displayed on thedisplay unit 505. Specifically, the image processing unit 134 includes adisplay-image generating portion 503 that generates image data on thebasis of the distribution information generated by the signal processingunit 133. The display-image generating portion 503 can perform theprocess of converting the intensity values at individual positions inthe distribution to luminance values and the process of generating guideinformation to be displayed together with the distribution information.Examples of the display-image generating portion 503 include a CPU, agraphics processing unit (GPU), and a field programmable gate array(FPGA) chip.

The image processing unit 134 may include an image storing portion 501that can store the distribution information output from the signalprocessing unit 133 and the image data generated by the display-imagegenerating portion 503. Typical examples of the image storing portion501 include storage mediums, such as a ROM, a RAM, and a hard disk. Thesignal storing portion may be either a single storage medium or aplurality of storage media.

The display unit 505 displays images on the basis of data output fromthe image processing unit 134. Examples of the display unit 505 includea liquid crystal display (LCD) a cathode ray tube (CRT), and an organicEL display. The display unit 505 may not be included in thesubject-information processing apparatus but may be a separate unitconnected to the subject-information acquisition apparatus. Examples inthis embodiment will now be described in detail.

Example 1

In this example, a case in which the characteristic information on thesubject 103 and the marker 111 are displayed will be described. The samesubject-information acquisition apparatus as shown in FIG. 1 can beused. The configuration of the marker 111 is shown in FIGS. 2A and 2B.FIG. 2A is a schematic side view of the holding member 109; and FIG. 2Bis a schematic top view thereof. The cup-shaped portion of the holdingmember 109 has a line marker 111 a with a lattice pattern. The marker111 a generates acoustic waves when irradiated with pulsed light emittedfrom the light source 121. For example, the marker 111 a is composed oflines made of acryl colored in gray with a width of about 0.5 mm.

In this example, when the subject 103 is irradiated with light whilebeing held by the holding member 109, the signal processing unit 133obtains received signals including a received signal caused by acousticwaves generated from the subject 103 and a received signal caused byacoustic waves generated from the marker 111 a. The signal processingunit 133 reconstructs an image on the basis of the received signalsincluding the two signal components to generate three-dimensionaldistribution information including the characteristic information on theinterior of the subject 103 and the information based on the marker 111.

Since an image indicating such distribution information is displayed,the user can easily determine the position of the holding member 109. Inother words, the user can determine the positions of the subject 103,the holding member 109, and the acoustic matching liquid 119 in theimage indicating the distribution information with reference to theposition of the marker 111 a in the image.

Without the marker 111 a, the position of the subject 103 in an imageobtained by receiving acoustic waves cannot easily be viewed, becausethe holding member 109 and the acoustic matching liquid 119 are made ofmaterials having acoustic impedances close to that of the subject 103.

In other words, providing the holding member 109 with the marker 111 a,as in this example, can enhance the visibility of the position of thesubject 103 in an image presented to the user.

The shape of the marker 111 a shown in FIGS. 2A and 2B is illustrativeonly, and a dotted marker 111 b shown in FIGS. 3A and 3B may beprovided. FIG. 3A is a schematic side view of the holding member 109;and FIG. 3B is a schematic top view thereof. The marker 111 may be in aline pattern, a radiating pattern, or a circular pattern.

Example 2

In this example, not only an image generated on the basis of acousticwaves but also an image captured by an optical image-capturing unit aredisplayed.

FIG. 4 is a schematic diagram of a subject-information acquisitionapparatus of this example. In FIG. 4, the same components as those inFIG. 1 are denoted by the same reference signs, and descriptions thereofare omitted. The subject-information acquisition apparatus of thisexample includes an optical image-capturing unit 301 on the supportingmember 113.

The optical image-capturing unit 301 is an image capturing apparatusthat captures an optical image, that is, a camera. The opticalimage-capturing unit 301 includes an image capturing apparatus capableof capturing a three-dimensional optical image, that is, atime-of-flight (TOF) camera. The optical image-capturing unit 301 isdisposed at a position at which images of the marker 111 (marker 111 a)and the state (the external appearance) of the subject 103 held by theholding member 109 can be captured from the lower part of the internalspace of the supporting member 113.

The image processing unit 134 displays an optical image (a photograph)captured by the optical image-capturing unit 301 and an image ofdistribution information input from the signal processing unit 133 onthe same screen. This display method allows the user to compare theexternal appearance of the subject 103 and the distribution informationon the interior of the subject 103 with each other, thus enhancing theuser visibility.

Example 3

This example shows a case having a mode of generating an image in whichinformation based on the marker 111 in the distribution information isreduced. In this example, the same subject-information acquisitionapparatus as that in FIG. 1 or 4 can be used.

In this example, before examination, the signal storing portion 401stores in advance received signals obtained by irradiating the holdingmember 109 with light in a state in which the holding member 109 doesnot hold the subject 103 (the subject 103 is not held in the holdingmember 109). In this case, the holding member 109 may be filled with,instead of the subject 103, a phantom member whose acousticcharacteristics are similar to those of human bodies or an acousticmatching member whose acoustic impedance is close to that of the holdingmember 109, such as an acoustic medium, for example, water and oil. Thisis for the purpose of reducing multiple reflection of acoustic wavesgenerated from the marker 111 in the holding member 109.

For examination, a received signal (a first received signal) in a statein which the holding member 109 holds the subject 103 (that is, thesubject 103 is present in the holding member 109) is input to the signalprocessing unit 133, as in Examples 1 and 2. The signal processing unit133 reads a received signal (a second received signal), stored in thesignal storing portion 401, in a state in which the subject 103 is notheld, and reduces signal components caused by the marker 111 using thefirst received signal and the second received signal. Typically, thesignal processing unit 133 subtracts the second received signal from thefirst received signal.

This process allows received signals in which signal components comingfrom the marker 111 are reduced to be obtained. The signal componentscoming from the marker 111 may not necessarily be completely deleted buthave only to be reduced. The reconstructing portion 433 reconstructs animage using the signal after the reducing process. This allowsdistribution information in which information based on the marker 111 isreduced (second distribution information) to be obtained. Not only thesecond distribution information but also distribution informationincluding the characteristic information on the subject 103 and themarker 111 (first distribution information) may be generated by themethod in Example 1.

FIGS. 5A and 5B schematically show the distribution information obtainedin this example. FIG. 5A is a diagram in which the greatest value in thez-direction is projected to an X-Y plane in a three-dimensional imageindicating the first distribution information; and FIG. 5B is a diagramin which the greatest value in the z-direction is projected to an X-Yplane in a three-dimensional image indicating the second distributioninformation. As shown in FIG. 5B, the image generated from the seconddistribution information does not show the marker 111. Displaying animage including no marker information allows the characteristicinformation on the interior of the subject 103 to be observed in detail.

The image processing unit 134 may execute at least one of a mode inwhich the first distribution information and the second distributioninformation are selected for display and a mode in which the firstdistribution information and the second distribution information aredisplayed side by side. The image processing unit 134 may execute a modein which only one of images of the first distribution information andthe second distribution information is displayed. Thus, the position ofthe subject 103 can be determined with an image including the marker 111like the first distribution information, and the interior of the subject103 can be viewed using an image in which marker information is reducedwithout the obstruction of marker information.

Example 4

An example including a mode in which an image in which information basedon the marker 111 is reduced, as in Example 3, will be described. Thisexample differs from Example 3 in a method for generating the seconddistribution information. The same subject-information acquisitionapparatus as in FIG. 1 or 4 can be used.

Also in this example, before examination, a received signal (the secondreceived signal) is obtained by irradiating the holding member 109 withlight in a state in which the holding member 109 does not hold thesubject 103 (the subject 103 is not held in the holding member 109).However, in this example, the reconstructing portion 433 generatesdistribution information (third distribution information) on a state inwhich the subject 103 is not present, that is, distribution informationthat does not include the characteristic information on the subject 103.The image storing portion 501 stores the third distribution information.

For examination, a received signal (the first received signal) in astate in which the holding member 109 holds the subject 103 (that is,the subject 103 is present in the holding member 109) is input to thesignal processing unit 133, as in Examples 1 to 3. The reconstructingportion 433 reconstructs an image on the basis of the first receivedsignal to generate the first distribution information.

The image processing unit 134 generates distribution information inwhich information based on the marker 111 is reduced using the firstdistribution information and the third distribution information.Typically, the image processing unit 134 subtracts the thirddistribution information from the first distribution information. Thisallows distribution information in which components based on the marker111 are reduced (the second distribution information) to be obtained.Also in this example, the signal components coming from the marker 111may not necessarily be completely deleted but have only to be reduced.

Also in this example, the image processing unit 134 may execute at leastone of a mode in which the first distribution information and the seconddistribution information are selected for display and a mode in whichthe first distribution information and the second distributioninformation are displayed side by side. The image processing unit 134may execute a mode in which only one of images of the first distributioninformation and the second distribution information is displayed. Thus,the position of the subject 103 can be determined with an imageincluding the marker 111 like the first distribution information, andthe interior of the subject 103 can be viewed using an image in whichmarker information is reduced without the obstruction of markerinformation. In this example, since the third distribution informationcan also be obtained, the third distribution information may bedisplayed.

In this example, the third distribution information may not necessarilybe generated before examination. If the second received signal is storedin the signal storing portion 401, the third distribution informationcan be generated during or after the generation of the firstdistribution information.

Example 5

This example shows a case in which guide information indicating theposition of the holding member 109 or the position of the subject 103 isgenerated for display. The same subject-information acquisitionapparatus as that of FIG. 1 or 4 can be used.

In this example, the image processing unit 134 generates guideinformation indicating the position of the holding member 109 or theposition of the subject 103 using received signals caused by the marker111. The generated guide information is superimposed on the firstdistribution information or the second distribution information obtainedby the processes described in Examples 1 to 4 for display.

The details will be described with reference to FIGS. 6A and 6B. FIGS.6A and 6B are schematic diagrams of images of distribution informationindicating tomograms in X-Y section. FIG. 6A schematically showstomograms of second distribution information without a guide; and FIG.6B schematically shows tomograms of second distribution information inwhich a guide is superimposed. FIG. 6B shows a circle 603 indicating thecontour of the holding member 109 serving as a guide indicating theposition of the holding member 109.

In FIGS. 6A and 6B, the left diagram shows a tomogram of the apex (lowerend) of the holding member 109, the central diagram shows a tomogram ofthe central portion of the holding member 109, and the right diagramshow a tomogram of a breast-wall-side portion.

Even if information based on the marker 111 is not displayed, thesubject 103 can be located by displaying guide information indicatingthe position of the holding member 109. Even if information based on themarker 111, like the first distribution information, is displayed, themarker 111 is sometimes not displayed depending on the slice position ofthe tomogram. Even in such a case, the subject 103 can be located byadditionally displaying the guide information.

The guide information can be generated using received signals containingsignal components coming from the marker 111. The guide information maybe generated not directly from received signals but from the firstdistribution information or the third distribution information.

The guide may not necessarily have a circular shape indicating thecontour, as shown in FIG. 6B. An area in the holding member 109 and anarea outside the holding member 109 may be distinguished by usingdifferent colors; any other guides that allow the user to locate thesubject 103 are possible.

Example 6

This example shows a marker that allows the orientation of an image tobe determined. The same subject-information acquisition apparatus asthat in FIG. 1 or 4 may be used.

FIGS. 7A and 7B are schematic diagrams of a marker 111 c of thisexample. FIG. 7A is a schematic side view of the holding member 109; andFIG. 7B is a schematic top view thereof. In FIGS. 7A and 7B, the marker111 c is at a position near the head of the examinee 101 and has a lineshape in top view in the axial direction of the body (a directionextending from the head to the feet).

This marker 111 c is effective when the holding member 109 has acup-shaped portion having a spherical surface. With an axisymmetricform, like a hemispherical cup, if a three-dimensional image indicatingdistribution information is rotationally displayed, the orientations ofthe three-dimensional images of the subject 103 displayed at individualtimings may not easily be determined intuitively. For example, it isdifficult to determine whether the images are viewed from the head sideor from the right.

However, the use of the marker 111 c asymmetric to the central axis (anaxis passing through the center of curvature) of the holding member 109makes it easy to determine which orientations the images are viewedfrom, because the view of the marker 111 c in the three-dimensionalimage varies with orientation.

Second Embodiment

Next, a second embodiment will be described. In this embodiment, anexample of setting a sound velocity in an acoustic medium (thepropagation velocity of acoustic waves) between the transducers 115 andthe holding member 109 using a marker will be described.

FIG. 8 is a schematic diagram of a subject-information acquisitionapparatus of this embodiment. The apparatus in FIG. 8 includes asound-velocity setting unit 201. Like components described in the firstembodiment are denoted by the same reference signs, and descriptionsthereof will be omitted.

In this embodiment, the sound-velocity setting unit 201 sets a soundvelocity using received signals caused by the acoustic waves generatedfrom the marker 111. The details will be described in the followingexamples. Also in this embodiment, information on the marker 111 and theguide may be displayed on an image to be presented to the user byapplication of the first embodiment. In other words, Examples 1 to 6 maybe combined to the second embodiment.

Example 7

In this example, a configuration in which the user can set a soundvelocity on the basis of an image of the marker 111 will be described.FIGS. 9A and 9B are schematic diagrams showing the configuration of amarker 111 d of the holding member 109. FIG. 9A is a schematic side viewof the holding member 109, and FIG. 9B is a schematic top view thereof.

In FIGS. 9A and 9B, a point-like marker 111 d is provided at the apex (alower end in the direction of gravity) of the cup-shaped portion of theholding member 109. The marker 111 d generates acoustic waves whenirradiated with pulsed light emitted from the light source 121. Forexample, the marker 111 d is a point made of acryl colored in gray witha diameter of about 0.5 mm. The marker 111 may have any shape, asdescribed in the first embodiment.

In this example, when the subject 103 is irradiated with light whilebeing held by the holding member 109, the signal processing unit 133obtains received signals including received signals caused by acousticwaves generated from the subject 103 and received signals caused byacoustic waves generated from the marker 111 d.

The importance of setting the sound velocity will now be described. Thesound velocity in the acoustic matching liquid 119 changes withtemperature. If the temperature of the acoustic matching liquid 119changes during examination, a deviation of an actual sound velocity froma set sound velocity may degrade the resolution of the image. This willbe described with reference to FIGS. 10A and 10B.

FIG. 10A is a schematic diagram of a two-dimensional image ofdistribution information taken along an X-Y section including the marker111 d in the case where the sound velocity in the acoustic matchingliquid 119 is properly set. FIG. 10B is a schematic diagram of atwo-dimensional image of distribution information taken along an X-Ysection including the marker 111 d in the case where a sound velocitydifferent from an actual sound velocity is set. If a proper soundvelocity is set, information on the marker 111 d is resolved as a point;if an improper sound velocity is set, the information is resolved as aring, thus degrading the resolution.

In this example, the sound-velocity setting unit 201 is configured to becapable to set an optimum sound velocity for the acoustic matchingliquid 119 in accordance with an instruction of the user so as to form ahigh-resolution image of the marker 111 d. Specifically, the signalprocessing unit 133 generates distribution information for prepareddifferent sound velocities in reconstructing an image on the basis ofobtained received signals. In other words, the signal processing unit133 generates a plurality of items of distribution information. Theimage processing unit 134 displays the plurality of items ofdistribution information on the display unit 505.

The user determines an image in which the marker 111 d has the highestcontrast while viewing the images of the plurality of items ofdistribution information and instructs the sound-velocity setting unit201 to set information on the sound velocity via an input unit (notshown). The sound-velocity setting unit 201 sets the information on thesound velocity as an optimum sound velocity to the signal processingunit 133 in response to the instruction from the user.

The signal processing unit 133 generates distribution information againusing the set optimum sound velocity. Alternatively, the signalprocessing unit 133 may output distribution information generated usingthe same sound velocity, which has already been obtained, as the optimumsound velocity to the image processing unit 134 again.

In the case where acoustic waves are to be obtained at a plurality ofdetection positions while the supporting member 113 is moving relativeto the subject 103, an optimum sound velocity may set on the basis of areceived signal obtained at one detection position (a first detectionposition), and the optimum sound velocity may be used at anotherdetection position (a second detection position). In other words, thesignal processing unit 133 may perform image reconstruction using areceived signal obtained at the second detection position and theoptimum sound velocity.

In this example, since a sound velocity that the user sets on the basisof an image based on the marker 111 d can be used, distributioninformation with enhanced resolution can be finally obtained. The marker111 d of this example is disposed at the apex of the holding member 109.This is for the purpose of preventing signal components caused byacoustic waves generated at the marker 111 d from being added todistribution information as artifacts. Disposing the marker 111 d atsuch a position allows the acoustic waves generated from the marker 111d to reach most of the plurality of transducers 115 earlier thanacoustic waves generated from the subject 103. This can decrease theproportion of superposed acoustic waves generated from the marker 111 d.

If an influence of the artifacts due to the acoustic waves generatedfrom the marker 111 d on the image is small, the marker 111 d may bedisposed at a position other than the apex of the cup-shaped portion.When the supporting member 113 is moved relative to the subject 103, thepositional relationship between the apex of the cup-shaped portion andthe plurality of transducers 115 also changes. In such a case, themarker 111 d may be provided at a position closest to the initialposition of the moving pattern of the supporting member 113.

In Example 7, received signals are obtained in a state in which thesubject 103 is held by the holding member 109 (during examination), andthe sound velocity is set on the basis of distribution informationgenerated using the received signals; this example is not limitedthereto. The sound velocity may be set on the basis of distributioninformation generated using received signals obtained in a state inwhich the subject 103 is not held by the holding member 109, such asdirectly before examination.

Example 8

This example shows a case in which the sound-velocity setting unit 201determines a sound velocity. In this example, the samesubject-information acquisition apparatus as that in FIG. 8 can be used.This example differs from Example 7 in which the sound-velocity settingunit 201 has the function of determining an optimum sound velocity. Anexample in which the marker 111 d as in FIGS. 9A and 9B is used will bedescribed. FIG. 11 is a flowchart for explaining the processes of thesound-velocity setting unit 201 and the signal processing unit 133 ofthis example.

In this example, first in S101, the signal processing unit 133 obtainsreceived signals obtained in a state in which the subject 103 is held bythe holding member 109.

In S102, the signal processing unit 133 generates distributioninformation at a plurality of different sound velocities prepared inadvance. In other words, the signal processing unit 133 generates aplurality of items of distribution information.

In S103, the sound-velocity setting unit 201 determines a sound velocityin the acoustic matching liquid 119 at which the contrast of the marker111 d is the highest from the plurality items of distributioninformation. For example, the sound-velocity setting unit 201 determinesdistribution information in which the half-value width of an X-axialintensity distribution in the area of the marker 111 d is the smallestas distribution information in which the marker 111 d has the highestcontrast among the plurality of items of distribution information. Asound velocity used in generating the selected distribution informationmay be determined as an optimum sound velocity.

In S104, the information on the optimum sound velocity determined by thesound-velocity setting unit 201 is set to the signal processing unit133, and the signal processing unit 133 generates distributioninformation using the optimum sound velocity and the received signal.Alternatively, distribution information generated using the same soundvelocity as the optimum sound velocity, obtained in S102, may be outputto the image processing unit 134 again.

In this example, since a sound velocity is determined without the userinputting an instruction on the sound velocity, as in Example 7,distribution information with high resolution can be obtained without aload on the user.

In obtaining acoustic waves at a plurality of detection positions whilethe supporting member 113 is moving relative to the subject 103, anoptimum sound velocity may be determined in the above flow on the basisof a received signal obtained at one detection position (the firstdetection position), and the optimum sound velocity may be used also atanother detection position (the second detection position). In otherwords, the signal processing unit 133 may perform image reconstructionusing the optimum sound velocity obtained from the distributioninformation at the first detection position and the received signalobtained at the second detection position.

In Example 8, received signals are obtained in a state in which thesubject 103 is held by the holding member 109 (during examination), andthe sound velocity is set on the basis of distribution informationgenerated using the received signals; this example is not limitedthereto. The sound velocity may be set on the basis of distributioninformation generated using received signals obtained in a state inwhich the subject 103 is not held by the holding member 109, such asdirectly before examination.

Modification of Example 8

The sound-velocity setting unit 201 may determine a sound velocity notfrom distribution information, as in FIG. 11, but directly from receivedsignals. In other words, the sound-velocity setting unit 201 maydetermine a sound velocity from time-axis changes in the intensity ofreceived signals output from the signal collecting unit 131.

Specifically, the sound-velocity setting unit 201 useschannel-by-channel time-series received signals from the signalcollecting unit 131 and information on light irradiation timing from aphotodetector (not shown). The distance between the marker 111 d and thetransducers 115 is a known distance. Thus, the sound-velocity settingunit 201 can calculate the time taken for acoustic waves from the marker111 d to reach the transducers 115 by regarding the light irradiationtiming as the timing of generation of acoustic waves from the marker 111d and by regarding a received signal that reaches first as a componentcaused by the acoustic waves generated from the marker 111 d. After thetime taken for arrival has been determined, the sound-velocity settingunit 201 can determine the sound velocity in the acoustic matchingliquid 119 from the time taken for arrival and the distance between themarker 111 d and the transducers 115.

The subsequent process is the same as S104 in FIG. 11. This method ofdetermining the sound velocity allows the sound velocity to bedetermined without the need for the user to enter an instruction on thesound velocity, thus providing high-resolution distribution informationwithout a load on the user.

Third Embodiment

Embodiments of the present invention can also be realized by a computerof a system or apparatus that reads out and executes computer executableinstructions recorded on a storage medium (e.g., non-transitorycomputer-readable storage medium) to perform the functions of one ormore of the above-described embodiments of the present invention, and bya method performed by the computer of the system or apparatus by, forexample, reading out and executing the computer executable instructionsfrom the storage medium to perform the functions of one or more of theabove-described embodiments. The computer may comprise one or more of acentral processing unit (CPU), micro processing unit (MPU), or othercircuitry, and may include a network of separate computers or separatecomputer processors. The computer executable instructions may beprovided to the computer, for example, from a network or the storagemedium. The storage medium may include, for example, one or more of ahard disk, a random-access memory (RAM), a read only memory (ROM), astorage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2013-227235 filed Oct. 31, 2013 which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A subject-information acquisition apparatuscomprising: a light source; a holding member configured to hold asubject and including a marker that absorbs light and generates anacoustic wave; at least one transducer configured to receive an acousticwave generated by irradiating the subject with light from the lightsource; a signal processing unit configured to obtain a photoacousticimage using a first received signal and a second received signal outputfrom the transducer; and an image processing unit configured to cause adisplay unit to display the photoacoustic image with guide informationindicating a shape of the holding member; wherein, in a state in whichthe subject is held by the holding member, the light source is adaptedto irradiate the subject and the marker and the at least one transducerreceives an acoustic wave generated by irradiating the subject and themarker and outputs the first received signal, wherein, in a state inwhich the subject is not held by the holding member, the light sourceirradiates the marker and the at least one transducer receives anacoustic wave generated by irradiating the marker and outputs the secondreceived signal, wherein the signal processing unit is configured togenerate the photoacoustic image on characteristic information on theinterior of the subject on the basis of the first received signal andthe second received signal, in a manner that information based on themarker in the photoacoustic image is reduced, and wherein the imageprocessing unit is configured to generate the guide informationindicating the shape of the holding member using a portion of the firstreceived signal or the second received signal due to the marker.
 2. Thesubject-information acquisition apparatus according to claim 1, whereinthe signal processing unit is configured to obtain a first photoacousticimage on the basis of the first received signal, and obtain thephotoacoustic image as a second photoacoustic image on the basis of thefirst and second received signals, and wherein at least one of the firstphotoacoustic image and the second photoacoustic image are selectivelydisplayed and the first photoacoustic image and the second photoacousticimage are displayed side by side.
 3. The subject-information acquisitionapparatus according to claim 1, wherein the second received signal isobtained when an audio matching member is held in the holding member. 4.The subject-information acquisition apparatus according to claim 1,further comprising: an optical image-capturing unit disposed at aposition where an optical image of a state in which the subject is heldby the holding member can be captured, wherein, the optical imagecaptured by the optical image-capturing unit is displayed.
 5. Thesubject-information acquisition apparatus according to claim 1, furthercomprising: a sound-velocity setting unit configured to set a soundvelocity in propagation pass of the acoustic wave generated from themarker on the basis of the portion of the first received signal or thesecond received signal due to the marker, wherein the signal processingunit is configured to generate the photoacoustic image using informationon the sound velocity set by the sound-velocity setting unit.
 6. Thesubject-information acquisition apparatus according to claim 1, furthercomprising: a supporting member, wherein the at least one transducerincludes a plurality of transducers, wherein the supporting membersupports the plurality of transducers, and wherein the plurality oftransducers is disposed on the supporting member so that the directionof the highest receiving sensitivity differs between part of theplurality of transducers and another transducer of the plurality oftransducers.
 7. The subject-information acquisition apparatus accordingto claim 1, wherein the holding member is a cup-shaped member.
 8. Thesubject-information acquisition apparatus according to claim 1, whereinthe marker has a line shape.
 9. The subject-information acquisitionapparatus according to claim 1, wherein the marker has a dot shape. 10.A method for displaying an image generated by a subject-informationacquisition apparatus on a display unit, the subject-informationacquisition apparatus comprising: a light source; a holding memberconfigured to hold a subject and including a marker that absorbs lightand generates an acoustic wave; at least one transducer configured toreceive an acoustic wave generated by irradiating the subject with lightfrom the light source; a signal processing unit configured to obtain aphotoacoustic image using a first received signal and a second receivedsignal output from the transducer; and an image processing unitconfigured to cause a display unit to display the photoacoustic imagewith guide information indicating a shade of the holding member; themethod comprising the steps of: in a state in which the subject is heldby the holding member, irradiating the subject and the marker with thelight and the at least one transducer receiving an acoustic wavegenerated by irradiating the subject and the marker and and outputtingthe first received signal, in a state in which the subject is not heldby the holding member, irradiating the marker with the light and the atleast one transducer receiving an acoustic wave generated by irradiatingthe marker and outputting the second received signal, generating thephotoacoustic image on characteristic information on the interior of thesubject on the basis of the first received signal and the secondreceived signal, in a manner that information based on the marker in thephotoacoustic image is reduced; and generating the guide informationindicating the shape of the holding member using a portion of the firstreceived signal or the second received signal due to the marker.
 11. Thedisplay method according to claim 10, further comprising the steps of:obtaining a first photoacoustic image generated on the basis of thefirst received signal, and obtaining the photoacoustic image as a secondphotoacoustic image generated on the basis of the first and secondreceived signals, and selectively displaying at least one of the firstphotoacoustic image and the second photoacoustic image or displaying thefirst photoacoustic image and the second photoacoustic image side byside.
 12. The display method according to claim 10, further comprisingthe steps of: capturing an optical image of a state in which the subjectis held by the holding member, and displaying the captured opticalimage.
 13. The display method according to claim 10, further comprisingthe steps of: setting a sound velocity in propagation pass of theacoustic wave generated from the marker on a basis of the portion of thefirst received signal or the second received signal due to the marker,wherein the photoacoustic image is generated using information on theset sound velocity.